The European patent publication EP-A-0271376 describes a process and apparatus for drying plums by supplying them to an oven on a conveyor belt, and by circulating hot air through the oven. The air temperature is uniform throughout the oven, and the temperature of the plums at the discharge is higher than their temperature at entering the oven.
The European patent publication EP-A-0079523 discloses a device and process for drying solid particles in a suspension, like e.g. urban sludges or non-edible waste. The drying installation disclosed in this document comprises a first upstream section in which the product is dried by circulating air which is heated in calorific heaters. The air that is discharged from this first section is led through a heat exchanger, mixed with discharged air from a second, downstream section and recirculated into the first section. In the second, downstream section, the product is dried by air that is heated by condensers of a heat pump, the evaporator of which is connected to the heat exchanger of the first section. The temperatures at which this drying installation operates are in the range of about 100.degree. C., and therefore much higher than necessary for drying vegetables.
Nowadays, vegetables to be dried after washing are supplied to a centrifuge, and dried therein in a discontinuous process. The drawbacks of this drying mode are that the product to be dried is damaged by the rotating drum and by the forces which the products exert on each other, and that the damaged and torn apart parts are left behind in the centrifuge, which may lead to the centrifuge becoming unbalanced and less hygienic due to possible material infection.